As an example of a semiconductor manufacturing process, there is a film forming process of depositing a predetermined thin film on a substrate by using a CVD (Chemical Vapor Deposition) method or the like.
When performing such a film forming process, for example, a vertical substrate treatment apparatus is used. For example, the vertical substrate treatment apparatus includes a process tube composed of an inner tube and an outer tube. A plurality of wafers held by a boat is carried into a cylindrical hollow portion of the inner tube. A gap between a lower end of the inner tube and a lower end of the outer tube is air-tightly sealed by a metal-made furnace opening flange formed in a circular ring shape.
In a case where a furnace opening member is formed at the lower end of the reaction tube and a gas introduction pipe is fixed to the furnace opening member, by-products may adhere to a low temperature portion such as a wall surface inside the furnace opening member of the lower portion of the reaction tube or the like. The adhered by-products may cause particles or the like.